Relative humidity indicator of the wet and dry bulb thermometer type



12, 1952 A. H. LAMB ET AL 2,606,446

RELATIVE HUMIDITY INDICATOR OF THE WET AND DRY BULB THERMOMETER TYPE Filed June 6, 1949 IN V EN TORS Patented Aug. 12, 1952 UNITED STATES PATENT OFFICE RELATIVE HUMIDITY INDICATOR OF THE WET AND DRY BULB THERMOMETER TYPE Application June 6, 1949, Serial No. 97,396'

6 Claims.

This invention relates to relative humidity indicators of the wet and dry bulb thermometer type, and more particularly to small and readily portable relative humidity indicators which include a motor-operated fan for decreasing the time required to obtain a wet bulb thermometer reading.

The conventional portable instrument for determining relative humidity with close accuracy is the sling psychrometer which comprises a wet and a dry bulb thermometer of mercury type on a supporting strip or plate which is pivotally connected to a staff or handle by which the operator rotates the thermometer assembly to promote the evaporation of water from the wet wick of the wet bulb thermometer. The relative humidity for any given set of temperature readings may be determined from a chart or a sliderule type of computer. Portable hygrometers with hair or silk threads as the humidity-responsive actuating elements are of relatively low accuracy and stability of calibration, and are not of practical utility in textile mills and other plants where the relative humidity is to be measured with an accuracy of i5% or better. A clear space of substantial size is required for operation of a sling psychrometer, and the thermometers may be broken by contacts with fixed objects when an attempt is made to obtain readings in confined spaces or closely adjacent to machines or materials.

Objects of the present invention are to provide portable hygrometers of the type stated which are mechanically rugged and of high accuracy, and which may be employed to measure relative humidity in small spaces or closely adjacent to machines and material. Objects are to provide hygrometers of the type stated which include a miniature motor and fan for establishing a current of air over the wet bulb thermometer. Objects are to provide hygrometers in which wet and dry bulb thermometers of bimetallic type are mounted upon a sheet metal supporting stand, and a bent plate is detachably or permanently secured to the base to support a miniature motor and fan, and to provide a chamber for receiving conventional dry cells for operating the fan motor. Other objects are to provide an accessory for attachment to the stand of a hygrometer of the type stated; the accessory being a plate supporting a miniature motor and fan, and cooperating with the hygrometer stand to form a chamber for receiving dry cells for energizing the fan motor.

These and other objects and the advantages of the invention will be apparent from the following 2 specification when taken with the accompanying drawings in which:

Fig. 1 is a perspective view of a relative humidity indicator embodying the invention; and

Fig. 2 is a perspective view, with parts in section, of the fan support and battery holder as seen from the front after removal from the metal stand.

In the drawings, the reference numeral l identifies the horizontal base section of a sheet metal stand upon which all parts of the hygrometer are mounted. The stand is formed by bending a metal plate of elongated rectangular form along parallel lines normal to the side edges of the plate, the first bend being at the rear end of the plate which is turned upwardly to form a vertical flange 2 with keyhole openings 3 by which the hygrometer may be supported by screws, not shown, set in a vertical wall. The metal supporting plate includes a vertical section 4 above the base section I, a rearwardly inclined section 5 above the vertical section 4, and finally a vertically extending section 6 provided with an elongated opening 1 in which the operator may insert his hand to carry the hygrometer, and with narrow openings 8 for receiving screw hooks, not shown, for supporting the hygrometer upon a wall or other vertical surface.

The stems 9, 9 and threaded mounting heads of bimetallic thermometers with casings l0, l9 respectively are passed through openings in the sloping section 5 of the sheet metal stand, and nuts, not shown, are threaded upon the mounting heads to secure the thermometers to the stand. The thermometer stems 9, 9' are normal to the sloping section 5 of the stand, and they are not shielded from any natural or forced air circulation since the metal stand has no side walls. A slide-rule or computer i2 is mounted upon the stand section 5 below the casings or dial heads 10, I0 01 the respective thermometers. The stem 9 of the dry bulb thermometer is in open air, but a tubular fabric wick I3 is slipped over the stem 9 of the wet bulb thermometer and passes through an opening in the screw cover [4 of a jar IE to dip into water in the jar. A sheet metal spring clamp or socket I6 is welded to the base section I to retain the water jar'on the base I.

In accordance with the invention, a miniature motor I! and fan I8 are supported upon the sheet metal stand to establish an air current over the stems of the wet and dry bulb thermometers. The motor I1 is mounted within the circumferentially split clamping ends l9, IQ of an arm 20 which is riveted or otherwise secured to one end means, the forward edges of the insulatingstrips being spaced from the flanges 2!, 23 to -provide grooves for receiving the edges of the vertical section 4 of the stand when the base section 22 of the resilient metal strap is momentarily flexed to spread the flanges 2|, 23' apart to slip over the supporting stand.

The length of the legs or end sections 2|, 23 of the strap is such that a compartment is formed between the strap and stand section 4 to receive a plurality, specifically four in the case of the illustrated embodiment, of flashlight dry cells 26 for energizing the motor l1. Circuit elements are mounted upon the insulating strips 24, 25 to connect the dry cells in series with each other and with the fan motor. A screw 21 is threaded through the plate end 2! and insulating strip 24 to form a control switch which may be turned inwardly to contact the base of the adjacent dry cell. A resilient metal strap 28 is mounted on the insulating strip 25 to connect the center electrode of the lower cell to the base of the upper cell. A stud 29 extends through the insulating strip 24 to engage the ctnter electrode of the adjacent cell, and a lead 30 extends from the outer end of the stud 29 to one terminal of the fan motor [1. The other motor terminal is grounded on the motor casing and arm 20, and thereby upon the U-shaped strap and the switch screw 21.

The fan motor is therefore energized when the switch screw 21 is turned to contact the base of the adjacent dry cell. Experience with one commercial embodiment of the invention has demonstrated that fan operation for approximately one minute will depress the temperature indication of the wet bulb thermometer to a stable minimum value. The current drain of the miniature motor is quite small, and the useful life of a set of dry cells is of the order of some ten hours. Operating costs are low as hundreds of readings may be made before a battery of cells is exhausted, and any economy which might theoretically be had by substituting a spring motor for the illustrated electric motor would be ofiset by the greater convenience and lower initial cost of the electrical motor and fan assembly. V

Bimetallic thermometers of high accuracy and of low time lag are available commercially, and relative humidity may be determined with an accuracy of 'l even when the illustrated apparatus is employed by persons who are not particularly skilled in the use of precision instruments. This high measuring accuracy is a further advantage which the apparatus has over the sling psychrometers since considerable experience and skill are required to obtain reliable and accurate relative humidity indications with such instruments.

The described detachable connection of the wide U-shaped strap 2l-23 to the sheet metal stand has the practical advantage that relative humidity indicators as herein described may be manufactured of the same standard components for sale either with or without the motor, fan and battery compartment assembly. It is possible, of course, to secure this assembly rigidly tothe sheet metal stand but the illustrated detachable construction is presently preferred.

It is to be understood that the invention is not limited to the particular construction herein shown and described as various changes which may be made fall within the spirit and scope of the invention as set forth in the following claims.

We claim.

1. In a portable hygrometer, the combination with a sheet metal stand comprising an initially rectangular and fiat plate bent on lines normal to the side edges of the plate to provide a horizontal base portion connected by a vertical section to a rearwardly inclined section, a pair of bimetallic thermometers supported on said rearwardly inclined section with the thermometer casings in front of said inclined section and the thermometer stems projecting through and normal to said inclined section, a tubular wick on one thermometer stem, a water container supported on said base section of the stand and said wick extending into the Water container, a motor and fan for establishing an air current over the stems of said thermometers, and means detachably secured to said sheet metal stand and supporting said motor and fan above a side edge portion of said horizontal base portion.

2. In a portable hygrometer, the invention as recited in claim 1, wherein said supporting means includes: a resilient metal strap of U-form and having flanges for engagement over the side edges of the vertical section of said sheet metal stand to anchor the metal strap thereto, an arm having one end securedto an end of said metal strap and means at the opposite end of said am for mounting said motor and fan.

3. In a portable hygrometer, the invention as recited in claim 2, wherein said motor is an electric motor, and said metal strap cooperates with said stand to form a compartment for receiving a plurality of cells for energizing said motor.

4. In a portable hygrometer, the invention as recited in claim 3, in combination with strips of insulating material mounted on the ends of said metal strap, and means including a switch and circuit elements mounted on said insulating material strips for connecting said cells in series with each other and with said motor.

5. In a portable hygrometer, the invention as recited in claim 4, wherein said switch for completing said circuit includes a screw adjustable through one of said strips into or alternatively out of engagement with an electrode of one of said cells.

6. For attachment to the side edges of a sheet metal stand supporting awet and dry bulb thermometer assembly; a metal strap of wide U-form with inturned flanges on the ends thereof for engagement over the opposite edges of the stand, the legs of the strap having a length spacing the base of the strap from the stand to form a compartment for receiving dry cells, an electric motor, an arm secured to said strap and supporting said motor, a fan driven by said motor, and circuit elements supported on said strap to connect said motor in circuit with dry cells inserted in said compartment; said circuit elements including a wire insulated from said strap and extending from one terminal of said motor to a stud insulated from said strap and positioned to be engaged by an electrode of a dry cell inserted in said compartment, the motor having a metal casing constituting a second motor terminal, said arm being metallic and constituting a circuit element grounding the motor casing on said strap,

2,606,446 5 and a metal screw adjustably threaded through file of this patent: 10

UNITED STATES PATENTS one end of said strap to contact or alternatively Number Name Date to break contact with a dry cell in said. compart-- 1,234,529 00mins July 24, 1917 ment' 1,309,531 McAdie July 8, 1919 ANTHONY LAMB 5 2,310,974 Lumm Feb. 16, 1943 EARL R. KEBBON.

FOREIGN PATENTS REFE C CITED Number Country Date The following references are of record in the 476,291 Great Br ta n 6. 9 

